The present invention especially relates to transducer heads or sensor heads for cardiography, tocography of cardiolocography for detecting the heart function or frequency of a fetus in the womb or the uterine activity referred to as toco, or for simultaneously detecting both parameters. The heart function or frequency of the fetus in the womb is normally detected by an ultrasonic transducer head externally attached to the pregnant woman's abdomen and fixed in position by means of an abdominal belt. The signals emitted by the ultrasonic transducer head and reflected towards the transducer head by the fetus are received by piezoelectric crystal transducer elements in the transducer head and filtered in a suitable manner. The ultrasonic transducer head must be secured in position by means of the abdominal belt on the abdomen directly above the fetal heart so as to guarantee a good transmission of ultrasonic signals between the housing and the tissue or vice versa.
Uterine activity can be detected by a transducer head referred to as a "tocodynamometer," the tocodynamometer being fastened to the woman's abdomen directly above the fundus uteri by means of an abdominal belt. Such a transducer operates as a dynamometer for measuring the respective forces applied by the abdominal belt and uterus to a penetrating prod. The prod projects slightly above the flat contacting surface of the housing and is normally connected to one or several strain measuring resistors. The toco transducer head determines the hardness and deformation of the uterus, and serves to detect the contraction frequency, contraction strength (amplitude) and contraction shape of the uterus. In addition, combined transducer heads for simultaneous ultrasonic supervision of fetal heart function and uterine activity (toco) are referred to as "cardiolocographic" transducer heads.
With regard to the fundamental function and construction of the above-described transducer heads, reference is made to prepublished EP-A1-300069, the disclosure of which is the basis for the disclosure of the present application. The known transducer heads typically have a flat, cylindrical housing with a substantially circular contacting surface which is brought into contact with the patient's abdomen. The housing can be slipped under the abdominal belt in a secured position, and can be fastened to the belt by bringing a button, which is provided on the side of the housing facing away from the abdomen, into engagement with a complementary buttonhole provided in the belt. If the patient changes her position, or if the belt slips relative to the abdomen, tensile forces acting transversely to the direction of the belt may produce (via the button on the housing) a tilting movement which impairs the contact between the contacting surface of the housing and the patient's abdomen; thus, it follows that when excessively high forces act on the head transversely to the direction of the belt, the signal to be measured will be impaired or, even worse, lost.
An additional problem of the known transducer head is that when the abdominal belt has been closed by means of the button it is impossible to displace the transducer head. If repositioning the transducer head is required, it will either be necessary to open the abdominal belt and close it again after the transducer head has been repositioned, or pull the whole abdominal belt and transducer head through below the patient's back, which will cause unreasonable strain to a pregnant woman.
Another problem arising in the handling of the known transducer head is that, during positioning of the transducer head and the subsequent belt closing operation, the person carrying out the treatment must use both hands for holding and attaching the transducer head and the belt. Still another disadvantage of the known transducer head is that the transducer head can only be secured in position with a belt that is specifically adapted to the transducer head and provided with adequate buttonholes.
EP-A2-0159434 discloses a clip-shaped electrode for use in the field of electrocardiography. The clip-shaped electrode has a structural design of such a nature that it encompasses the patient's extremities and brings an electrode into spring-type contact with the extremities. Measurements on the abdomen cannot be carried out by this type of electrode.
DE-A1-3444635 discloses a transducer head for monitoring a patient's heart and circulation, the housing of the transducer head being adapted to be fastened to the patient's thorax by means of a belt. The way in which the housing of the transducer head is secured in position relative to the belt is not explained in detail.